Compounds having the basic skeleton of quinoline-carboxylic acid are known to include many compounds useful as synthetic antimicrobials for their excellent antimicrobial activities and broad antimicrobial spectra. Among such compounds, norfloxacin (JP 53-141286 A), enoxacin (JP 55-31042 A), ofloxacin (JP 57-46986 A), ciprofloxacin (JP 58-74667 A), tosufloxacin (JP 60-228479) and the like are widely used in clinical practice as therapeutic agents for infectious diseases.
These compounds, however, are not sufficient yet in antimicrobial activities, intestinal absorption and metabolic stability, and still involve many problems to be solved, such as reductions of phototoxicity and cytotoxicity both of which are specific to quinolinecarboxylic acid and its derivatives. Recently, the emergence of resistant bacteria to these medicaments has also raised a problem.